Different designs of fuel injection systems are disclosed in the following publications:
German published patent application No. 32 27 742 (corresponding to U.S. Pat. No. 4,566,416); U.K. Pat. No. 2 165 895 (corresponding to U.S. Pat. No. 4,633,837; German published patent application No. 31 26 393 (corresponding to U.K. Pat. No. 80 21 836; German published patent application 29 07 279; French published patent application No. 2 546 237 (corresponding to U.S. Pat. No. 4,535,742) and French patent specification No. 1,176,110 (corresponding to U.K. Pat. No. 818 197).
In German published patent application No. 32 27 742 and U.S. Pat. No. 4,566,416 an injection system is disclosed employing injectors provided with an accumulator volume or chamber with a volume substantially larger than the maximum volume of fuel injected during each injection event. This accumulator chamber is located in the injector body upstream of the seat of the injector needle valve. The injection orifices are located downstream of this seat. These orifices communicate with the combustion chamber of the related internal combustion engine. The fuel stored in the accumulator chamber under high pressure is partly discharged through the injection orifices during each injection event with a simultaneous pressure drop in the accumulator chamber. The injector accumulator communicates with the high pressure fuel supply line of the injection system by means of a restricted passage or orifice. The orifice, due to its small cross-sectional flow area, prevents the formation of noticeable pressure waves in the fuel supply lines during each injection event. Such pressure waves would highly affect the uniform fuel distribution in a multicylinder engine and the stability of the injection events of a single injector from cycle to cycle.
To obtain good engine performance with respect to engine power, efficiency and emissions, a very uniform fuel distribution from cylinder to cylinder must be achieved in a multicylinder engine at each engine operating point. The same holds true for each injector from cycle to cycle. In addition to said orifice between each injector accumulator and the fuel supply line, a plenum fuel chamber communicating with the fuel supply lines of all injectors of the injection system is provided in order to achieve the desired uniform fuel distribution. Due to its relatively large volume, the plenum chamber evens out the pressure pulsations created by the high pressure fuel supply pump and thus creates a constant pressure level for all injectors. At different points in the engine operating range, different fuel injection pressures are required. As an example, it is advantageous to use a low injection pressure at low engine load and at idling and a high injection pressure at high engine load and high speed.
In a passenger car engine, transient speed and load conditions are the most often encountered situation, and the injection system pressure must be able to rapidly respond to the warming driver demands. It must be possible to rapidly increase and drop the fuel pressure in the plenum chamber. Due to its large volume, this is a difficult task to accomplish.
In the injection system disclosed in UK Pat. No. 2 165 895 and the corresponding U.S. Pat. No. 4,633,837 the fuel metered by a high pressure pump is delivered to a fuel manifold. Fuel lines lead from this manifold to the injectors. In each line section connecting one injector to the fuel manifold there is placed an electrically operated on/off valve. To allow for the momentary injection of fuel by an injector, the on/off valve must be opened. The injector needle valve will subsequently be opened against the closing bias force of a spring by the fuel pressure propagating from the on/off valve to the needle valve seat. To terminate each one of such momentary injection events, the on/off valve must be closed to allow the fuel pressure at the injector to drop below the bias force of the needle valve spring which consequently closes the injector needle valve. In the period between two injection events of one injector the pressure in the line section between the on/off valve to the injection valve seat is lower than the injector needle valve opening pressure and thus substantially lower than the injection pressure during the injection event. The actual injection pressure at the end of the injection event is low, according to the closing force of the injector needle valve spring, which results in poor fuel atomization and increased polluant emissions of the related internal combustion engine.
In the injection system of the German Pat. No. 31 26 393 fuel is delivered under high pressure to a fuel chamber similar to the plenum chamber disclosed in the aforementioned German Pat. No. 32 27 742. From this chamber fuel is fed by fuel lines of a small inner diameter to the injectors of the injection system. The pressure drop at each injector during each injection event is used to control the fuel delivered by each injector into the combustion chamber of the related internal combustion engine. This last system appears to have the same basic disadvantage as the system disclosed in German Pat. No. 32 27 742 discussed earlier, namely poor response of the system pressure during transient engine operation.